Portable x-ray images are used to aid in assessing pathological changes and/or tube/line placement in critically ill patients in the U.S. Over 50% of portable examinations are performed in Critical Care Units (Intensive Care and Coronary Care). The remaining portable exams are performed on the medical or surgical floors or in the Emergency Room. Most patients in a Critical Care Unit have an x-ray procedure at least once per day. The primary portable exam type is AP (anterior-posterior) chest (80% of portable procedures) followed by abdomen and bone. The portable chest radiography market is expected to grow 20% in the United States over the next 5 years.
The technologist's problems in portable radiography are well known: maneuverability of the portable x-ray generator, carrying a large number of cassettes, x-ray tube positioning and determination of proper technique. The variability in positioning the x-ray tube results in different techniques between exams. This sometimes results in over or underexposure so that the radiologist requires an exam to be repeated. The average repeat rate is on the order of 5% to 10%.
The films that are generated while the patient is in a Critical Care Unit are kept in either the radiology department or in the unit. Typically, the most recent films are put on an alternator for easy access and review. Consultation about the procedure occurs where the films are located, requiring either the radiologist or the clinician to go to the films. At some institutions, a double film protocol is used in order to give both the radiologist and clinician easier access to the image.
As radiologists read portable exams, the most current film is compared to previous films to assess changes in the patient's condition. The variability in exposure with current film/screen combinations adds to the difficulty in the assessment of changes that are due to illness.
The clinicians in the Critical Care area often need immediate access to the portable films in order to check proper tube placement. They often "borrow" the film from the radiology department before the radiologist has a chance to read it. Sometimes these films are not returned and a report is not generated; thus the hospital has lost revenue for that exam.
As the population grows older, more people will be hospitalized and require surgery and critical care. Thus the number of portable examinations will increase; the need for better quality and faster portables will increase and hospitals will be in a position to justify the allocation of funds for new systems and additional generators specifically for portable procedures.
In the decades after the end of World War II, there were significant advances in phosphor materials. These advances made high speed electronic imaging possible. Research at Eastman Kodak Company, Rochester, N.Y., led to the first demonstration of a scanned storage phosphor radiographic system. This system was originally patented in 1975 and reissued as U.S. Pat. No. Reissue 31,847, reissued Mar. 12, 1985, to Luckey. In the storage phosphor system disclosed a storage phosphor is exposed to an x-ray image of an object, such as the body part of a patient, to record a latent x-ray image in the storage phosphor. The latent x-ray image is read out by stimulating the storage phosphor with relatively long wavelength stimulating radiation such as red or infrared light produced by a helium neon gas laser or diode laser. Upon stimulation, the storage phosphor releases emitted radiation of an intermediate wavelength, such as blue light, in proportion to the quantity of x-rays that were received. To produce a signal useful in electronic image processing the storage phosphor is scanned in a raster pattern by a laser beam deflected by an oscillating or rotating scanning mirror or hologon. The emitted radiation from the storage phosphor is reflected by a mirror light collector and detected by a photodetector such as a photomultiplier to produce an electronic x-ray image signal. Typically the storage phosphor is translated in a page scan direction past the laser beam which is repeatedly deflected in a line scan direction perpendicular to the page scan motion of the storage phosphor to form a scanning raster pattern of a matrix of pixels.
The x-ray image signal can then be viewed as a visual image produced by a softcopy display device, such as a video display (CRT, LCD) or a hardcopy display device, such as a x-ray film printer (laser printer, CRT printer, thermal printer).
There has been proposed in copending U.S. application Ser. No. 981,144, filed Nov. 24, 1992, inventors Godlewski et al., a quality control workstation (QCW) linked to a storage phosphor reader. The quality control workstation provides a radiology technologist with several functions, including checking images acquired from a storage phosphor reader (or other sources of digital radiographic images), correcting patient information and x-ray exam information, adjusting image parameters, such as image orientation and window width and leveling, routing acceptable exams and images to designated destinations (such as remote high resolution workstations, magnetic or optical archival image storage, radiographic laser, CRT, thermal printers).
The QCW image processing software uses four Look Up Tables (LUTs) in order to transform the image data (which is in digital form) and present it to the user on a video display. The four LUTs are:
______________________________________ the gamma lut (12 bit in, 8 bit out) the window/level lut (12 bit in, 12 bit out) the preference lut (12 bit in, 12 bit out) the crt lut (12 bits in/8 bits out) ______________________________________
The preference lut is used to give the image an overall appearance, i.e. a "regular" look (white bones), black bone, and high contrast. The gamma lut is used to correct for the non-linear response of the display device (i.e. the video display tube). The window/level lut is used to select a region of interest within the image, where level adjusts the brightness of the image, and window adjusts the contrast of the image.
The QCW image processing software previously performed the window/level function as follows:
The user requested that a specific image be displayed, for the purpose of verifying image quality; poor images could be windowed and leveled. PA1 To change the window width and level values for the displayed image, the user would push the left mouse button, while simultaneously moving the mouse (the position of the mouse cursor is sensed, in order to derive the window and level values, with the x axis representing level, and the y axis representing window). This cycle took approximately one to two seconds per re-display of the image with the most recently sensed window and level values. To accomplish this, the image processing software would cascade the tonescale, window/level, and gamma LUTs, creating the crt lut. The data representing the currently displayed image would then be mapped to display values through the crt lut. At this point the reprocessed image would be displayed on the video display tube. The three LUTs are cascaded to form the crt LUT, which the image pixels are mapped through, in order to give the desired result on the video display tube. PA1 a memory for storing digital radiographic images; PA1 a video display; PA1 a hardware color lut memory; PA1 a user input device; and PA1 a digital computer, wherein real-time window/leveling is effected by a user, (a) using the user input device to display a selected radiographic image from said memory, (b) using the user input device, changing the window width and level of the displayed image until a satisfactory image is obtained, each change in window width and level being effected by cascading a preference lut, a window/level lut and a gamma lut into a crt lut by means of software routines of said digital computer, thereafter the crt lut is loaded into the hardware color lut memory, while reserving the color cells used in display borders, scroll bars, and other non-display areas, the radiographic image from said memory being processed by said hardware color lut memory for display on said display.
Such a software intensive window/leveling technique has been found to provide slow feedback to the workstation user. As a result, the user desired values for window and level were often difficult to achieve. The slowness of response is due partially to the fact that software runs on the control computer and shares computing time with all the other applications that run on the computer. These other applications are chores that the computer must maintain, such as keeping track of keyboard input and reading data from disc.
There is thus a problem in the display of a radiographic image on a workstation to rapidly effect tonal changes in the image by window/leveling inputs by a user of the workstation.